EARTH FAULT INDICATOR
INSULATION OK
Earth fault indicator lamp
∞ MΩ
INSULATION RESISTANCE TO EARTH
Ph A
Ph B
Ph C
Phase earth fault indication. Bright phase = fault on that conductor.
440V IT SYSTEM
FEEDER CIRCUITS — CLICK TO ISOLATE/RESTORE
ISOLATION LOG & PROCEDURE
PROCEDURE:
1. Note lamp status (steady/flash)
2. Note phase indicator
3. Open feeders one by one
4. Lamp OFF = fault in that feeder
5. Sub-isolate to find equipment
6. Clear fault, restore circuit
1. Note lamp status (steady/flash)
2. Note phase indicator
3. Open feeders one by one
4. Lamp OFF = fault in that feeder
5. Sub-isolate to find equipment
6. Clear fault, restore circuit
ISOLATION LOG
WHY IT SYSTEMS ON SHIPS
IT = Insulated Terra — neither supply conductor is earthed.
Key advantage: A single earth fault does NOT cause a circuit breaker to trip. Power continues to essential services (propulsion, steering, navigation) while the fault is safely located and cleared.
Shore supply (TN/TT): One neutral is earthed — first fault causes breaker trip. Unacceptable for critical ship systems.
Key advantage: A single earth fault does NOT cause a circuit breaker to trip. Power continues to essential services (propulsion, steering, navigation) while the fault is safely located and cleared.
Shore supply (TN/TT): One neutral is earthed — first fault causes breaker trip. Unacceptable for critical ship systems.
INSULATION RESISTANCE GUIDE
■ > 1 MΩ — EXCELLENT: No action required
■ 500kΩ–1MΩ — GOOD: Monitor regularly
■ 100–500 kΩ — MARGINAL: Plan maintenance
■ 50–100 kΩ — LOW: Locate fault soon
■ 10–50 kΩ — FAULT: Isolate and clear
■ < 10 kΩ — SERIOUS: Immediate action
SCENARIO STATUS
Fault Circuit
HIDDEN
Circuits Isolated
0
Fault Located
NO